Customers not exactly silent when screwed (7)
I believe the answer is:
clients
'customers' is the definition.
(I know this)
'not exactly silent when screwed' is the wordplay.
'not exactly' becomes 'c' (short for 'circa').
'when screwed' is an anagram indicator (the order of letters is screwed up).
'silent' with letters rearranged gives 'lients'.
'c'+'lients'='CLIENTS'
(Other definitions for clients that I've seen before include "Customers of the professions" , "Stencil (anag)" , "Consumers" .)